Dray: Agreed - though as you suggest, the DMZ solution is not ideal. I've seen that link (though the 8800NL R2 model it refers to is not the one I have). Stil, the PPP Half Bridge mode looks like it would be the best option, but I can't get it working. Whether that's my misconfiguration of the firewall, or oddities with Sky authenticaiton, I can't say!
Chrysalis: I've had a look but can't find the one you mean. If you do get a chance to post the link, that would be very handy. Though as Dray asked - was that for Sky ADSL?